title: 5-HT stimulation of heart rate in Drosophila does not act through cAMP as revealed by pharmacogenetics.
abstract: The fruit fly, Drosophila melanogaster, is a good experimental organism to study the underlying mechanism of heart rate (HR) regulation. It is already known that many neuromodulators (serotonin, dopamine, octopamine, acetylcholine) change the HR in Drosophila melanogaster larvae. In this study, we investigated the role of cAMP-PKA signaling pathway in HR regulation and 5-HT positive chronotropic action. In order to obtain insight into the 5-HT mechanism of action in larvae cardiomyocytes, genetic and pharmacological approaches were used. We used transgenic flies that expressed the hM4Di receptor [designer receptors exclusively activated by designer drugs (DREADDs)] as one tool. Our previous results showed that activation of hM4Di receptors (modified muscarinic acetylcholine receptors) decreases or arrests the heart from beating. In this study, it was hypothesized that the positive chronotropic effect of serotonin [5-hydroxytryptamine (5-HT)] are mediated by serotonin receptors coupled to the adenylyl cyclase pathway and downstream cAMP and PKA activity. Activation of hM4Di by clozapine-N-oxide (CNO) was predicted to block the effects of serotonin by inhibiting adenylyl cyclase activity through Gαi pathway activation. Interestingly, we found here that manipulation of adenylyl cyclase activity and cAMP levels had no significant effect on HR. The ability of hM4Di receptor activation to slow or stop the heart is therefore likely mediated by activation of GIRK channels to produce hyperpolarization of cardiomyocytes, and not through inhibition of adenylyl cyclase.
authors.affiliation: Department of Biology, University of Kentucky, Lexington, Kentucky;
authors.forename: Zana R
authors.initials: ZR
authors.lastname: Majeed
authors.forename: Charles D
authors.initials: CD
authors.lastname: Nichols
authors.forename: Robin L
authors.initials: RL
authors.lastname: Cooper
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D030801:Animals, Genetically Modified; D003024:Clozapine / Q000031:analogs & derivatives / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004330:Drosophila; D006339:Heart Rate / Q000187:drug effects*; D007814:Larva / Q000187:drug effects / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000494:pharmacology; D010597:Pharmacogenetics / Q000379:methods; D011976:Receptors, Muscarinic / Q000378:metabolism; D011985:Receptors, Serotonin / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D018377:Neurotransmitter Agents; D011976:Receptors, Muscarinic; D011985:Receptors, Serotonin; D012701:Serotonin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D003024:Clozapine; C079149:clozapine N-oxide
keywords: 5-HT; CNO; M4D receptor; PKA; adenylyl cyclase